Hard core safety for French nuclear

18 November 2011

France's nuclear installations are confirmed as being safe - but nevertheless an expert report submitted to the safety regulator is urging the adoption of a set of 'hard core' safety requirements to ensure facilities remain stable in the event of beyond-design basis external events.

The recommendation comes in an expert report released by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and Autorité De Sûreté Nucléaire (ASN) which considers the findings of the complementary safety assessments – known as 'stress tests' in other countries - carried out at French nuclear installations in response to the Fukushima accident. The ISRN's in-depth report provides strong recommendations for France's future nuclear safety regime.

In the report, ISRN proposes a new set of 'hard core' safety requirements to ensure the protection of safety-critical structures and equipment to ensure that vital functions can be maintained in the face of events beyond the design basis of the plant, such as earthquakes, fires, or the prolonged loss of power or emergency cooling.

The IRSN has drawn three major conclusions from the findings of the studies. Firstly, it recommends that all French nuclear operators work quickly to address the few gaps in compliance with current safety requirements revealed at some sites, noting that corrective actions are already underway. Although taken alone they would not directly compromise safety, these discrepancies would be likely to introduce an area of weakness in the event of an accident sequence, and therefore the IRSN has recommended all French nuclear operators complete by the end of next year reviews of compliance of all equipment needed in the event of loss of external energy supply or cooling.

Secondly, the IRSN says, the standards referred to in some safety areas need to be updated to reflect current experience, particularly with respect to earthquakes. Such changes would normally be incorporated at the time of regular ten-yearly reviews carried out at French plants, but the IRSN report recommends taking advantage of such new knowledge sooner rather than later. Thirdly, events in Japan have shown that the occurrence of natural phenomena that go beyond the basis of plant design, causing effects on multiple facilities and over a prolonged duration, cannot be ruled out.

It is in response to these conclusions that IRSN recommends a new 'hard core' approach to safety, in which further studies would be needed to identify extra measures needed at each specific site, particularly to deal with seismic hazards and flooding. Operators should also identify all safety-critical structures, systems and components essential to providing defence in depth in a severe accident situation, and to propose measures to strengthen such measures to withstand events beyond the basis of the plant's design. This would serve to protect vital structures and equipment against such natural hazards while ensuring their robustness and independence relative to those facilities available during "normal" plant operations which could be made unavailable in extreme events.

Easier for EPR

The same reasoning applies to the new-generation Areva EPR unit currently under construction at Flamanville, although the very nature of the reactor design and the fact that the plant is still under construction will make it easier to incorporate any modifications.

The EPR design already takes into account the possible effects of a combination of onslaughts to a greater extent than in currently operating reactors, the IRSN notes, and systems to manage accident situations, including serious ones, are already incorporated in the design. The EPR design, for example, includes measures such as additional diesel generators in case of a station blackout situation, additional water reserves, a double containment with a steel liner in the inner containment, and a so-called core catcher which guarantees containment integrity for a long time in the event of an accident leading to a core melt.